Manufacture of burnt lime by burning calcium carbonate or temperatures ranging from approximately 900.degree. to 1300.degree. C. is known. That burning decomposes CaCO.sub.3 into CaO and CO.sub.2 and causes structural alterations in the product which result in a reduction in volume known as shrinking. This volume reduction varies from about 10 to about 60 percent depending upon the burning temperature and the impurity content of the raw CaCO.sub.3 material.
Low burning temperatures--about 900.degree. C.--result in insignificant shrinkage and a very porous product. Also, the reaction time for CO.sub.2 expulsion is so slow that it is not technically feasible to operate at such low temperatures. CO.sub.2 expulsion at higher temperatures is faster--takes place at sufficiently high velocity--but under these conditions the material shrinks more, which causes a reduction in the porosity of the product.
Normally, the product is cooled after burning. Cooling often transforms the product into Ca(OH).sub.2 by reaction--slaking--with water.
Depending upon operating conditions, it is sometimes desirable that slaking occurs quickly; but it may also be desirable that slaking occurs slowly. Slaking velocity is dependent upon reactivity of the burnt product. Reactivity is dependent on porosity which again is primarily dependent upon burning temperature, burning time and impurity content of the raw material. In order to produce a product having a certain reactivity, manufactured from a raw material having a fluctuating impurity content, compensating adjustments for the burning temperature and for the burning time are required.
Previously, to achieve a desired reactivity of the product when burning lime, a current, discontinuous, manual quality control had to be carried out for the burnt lime, which included mixing a specified amount of water having a certain temperature, for example 20.degree. C., with a specified amount of burnt lime having a certain fineness and temperature. This is slaking of a sample under controlled conditions. Because the hydration reaction is exothermic, the reactivity of the burnt lime can be determined either by measuring the time necessary for achieving a given rise in temperature or by measuring the temperature increase achieved during a given time.
If the reactivity is poor, the material has been burnt too hard. Consequently, the supply of fuel to the kiln and the material residence time in the kiln must be reduced.
Burning of MgCO.sub.3 and dolomite involve similar considerations.
It is desirable to maintain optimum operating conditions to produce a homogeneous product having a desired reactivity and to bring about automatic control of the burning conditions.
Continuous analyses and reactivity determinations of liquid products is known. German Patent Specification No. 468,912 relates to a method of analyzing a liquid chemical product based on its heat of reaction by reaction with a liquid reagent. The chemical product and the reagent flow through corresponding, separate, intermediate receivers where their temperatures are measured. Then, they are mixed in a reactor functioning as a calorimeter; and temperature is measured. Temperature increase is a function of the heat liberated in the reactor and serves to determine the concentration of the product.
U.S. Pat. No. 3,716,333 relates to a method of analysis for determining the concentration of Mg and K in which heat exchange due to reaction with a suitable reagent is used to determine concentration. In this method, sample and reagent are fed at a constant temperature to a reaction chamber immersed in a water bath, and the temperature difference between water bath and reaction chamber is used to measure concentration.
Isothermic calorimetry is a well known technique of analysis in which the content of the calorimeter is maintained at a constant temperature. Such a technique is described in U.S. Pat. Nos. 3,841,155 and 3,994,164 and German OS No. 2,355,952. According to this process, a calorimeter is immersed in a water bath having a constant temperature T.sub.bath. The calorimeter has a heat exchanger so that its contents can be maintained at a constant temperature T.sub.cal higher than T.sub.bath. If sample and reagent are continuously fed into the calorimeter at a constant temperature and flow rate and if the heat liberated or consumed by the heat exchanger is regulated so that the temperature difference T.sub.cal -T.sub.bath is constant, the quantity of heat liberated or consumed by the heat exchanger can be used as a measure of the thermal efficiency of the reaction between sample and reagent. The sum of the heat from the reaction and the heat from the heat exchanger is maintained constant.
I have invented a process and apparatus in which the reactivity of solids is utilized and employed for controlling their burning process.